Even though there are still HIV-infected vaginal cells present when the viral load in plasma is undetectable, there is not enough virus to transmit, aidsmap reports. Publishing their findings in The Journal of Clinical Investigation, researchers studied HIV-infected female mice engineered to have human immune systems.

After treating the mice with antiretroviral (ARV) therapy, the researchers saw a greater proportional viral load drop in the animals’ plasma than in cervico-vaginal secretions. There were still about 80 copies per million cells of cell-associated HIV RNA in the female reproductive tract.

The researchers created a lab test in which they exposed vaginal cells to immune cells from blood or vaginal fluid taken from the treated mice. When the immune cells were taken from mice two weeks after the animals were started on ARVs, cells from neither source led to infection in the other cells. When the cells were taken after one week of treatment, the virus did transmit between cells.

Then the scientists took two sets of five HIV-negative female mice and exposed them vaginally to either 5,000 or 10,000 HIV-infected immune cells. None of the mice that received the smaller dose of cells was infected, compared with two of the group receiving the larger dose. But 5,000 exceeds the number of HIV-infected cells found in doses of either treated blood or treated vaginal fluid.

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To read the study, click here.